It is known in principle that compact circuit breakers (MCCB=Molded Case Circuit Breaker) are designed, for example, in accordance with the principle of magnetic repulsion or the interruption or disconnection of the contacts. In this case, the contacts open before the expected peak value of the short-circuit current is reached. By virtue of the disconnection of the contacts, the thermal loading and mechanical loading owing to the sudden short-circuit current of the system components, which can occur during a short circuit, are reduced considerably. A compact circuit breaker is used, for example, to implement a dual function, namely protection of an installation from overload and short-circuit currents and protection of lines and electrical operating means from damage as a result of ground faults, for example.
In order to protect an installation from overload currents or short-circuit currents, the compact circuit breaker, which can also be referred to as a thermal magnetic circuit breaker, has a thermal magnetic trip unit (TMTU). The thermal magnetic trip unit has a thermal tripping apparatus in order to protect the electrical circuit or an electrical apparatus from damage owing to an overload, and a magnetic tripping apparatus in order to protect the electrical circuit or an electrical apparatus from damage owing to a short circuit.
A short circuit and in particular an electrical short circuit is generally known as an accidental or unintentionally occurring conductive connection between two or more conductive parts and primarily between two nodes of the electrical circuit, as a result of which the electrical potential differences between these conductive parts drop to a value equal to zero or close to zero.
In particular, in respect of a compact circuit breaker, a short circuit is an abnormal connection between two isolated phases, which are intended to be isolated or insulated from one another. A short circuit results in the presence of an excessive electrical current, namely an overcurrent, which can result in damage to, overheating of, a fire in or even an explosion in the electrical circuit and/or the consumer. An overload is a less extreme state in comparison with the short circuit and is rather a long-term overcurrent state.
It is furthermore known in principle that the thermal tripping apparatus has, for example, a bimetallic element consisting of at least two metal strips rolled one on top of the other, each having different coefficients of thermal expansion. The electric current flows via a corresponding heating winding or along a tapering current conduction path for heating this bimetallic element, for example, wherein, owing to the different coefficients of thermal expansion of the metal strips, the bimetallic element is bent or curved when corresponding thermal energy is applied.
Owing to the bending movement of the bimetallic element, for example, control contacts are actuated or a latching mechanism of a circuit breaker is unlatched. The magnetic tripping apparatus or the electromagnetic tripping apparatus is constructed, for example, in such a way that, in the event of the occurrence of a short circuit or a short-circuit current, the electric current flowing via a current-conducting element is so great that a yoke element arranged on the current-conducting element generates a magnetic field, as a result of which, in turn, an armature element is attracted, for example.
Owing to the movement of the armature element, a latching mechanism of the circuit breaker is unlatched without delay, for example. The armature element or the armature is held in position in a known manner by a spring and in particular a tension spring, with the result that a movement of the armature element in the direction of the yoke element counter to the tensile force or spring force of the spring therefore can only take place in the case of the occurrence of a defined magnetic field strength and therefore a correspondingly triggering short-circuit current intensity. Compact circuit breakers are preferably power circuit breakers which can be switched on again after tripping owing to an overload or a short-circuit current.
In particular in respect of the different rated currents of the electrical circuit in which the electrical switch, in particular the compact circuit breaker, is arranged for interrupting a current flow of an electric current, it is necessary to be able to set the tripping characteristic or the tripping values, in particular as regards the response time, of the compact circuit breaker and in particular the thermal magnetic trip unit of the electrical switch. In the case of the presence of a thermal magnetic trip unit with one or more tripping shafts, it is known in principle that an adjustment of the tripping torque can take place by means of an axial movement or axial displacement of the individual tripping shafts. Such an axial displacement of the tripping shafts and in particular of the thermal tripping shaft and also of the magnetic tripping shaft is caused in this case, in a known manner, by a rotation or rotary movement of a setting element, such as a setting knob, for example. The corresponding knob is in this case connected to the tripping shaft via a pin.
In order to implement simple fitting of the individual parts, and also to take into consideration corresponding manufacturing tolerances of the individual component parts, it is possible in a known manner to arrange the individual component parts with respect to one another, or to connect them to one another, whilst maintaining corresponding interspaces or spacings. Such interspaces do, however, disadvantageously cause imprecise positioning of the individual component parts and in particular of the individual tripping shafts with respect to one another and also with respect to the remaining component parts of the thermal magnetic trip unit, which therefore in turn can result in imprecise setting or adjustment of the thermal magnetic trip unit and in particular the tripping shafts of the thermal magnetic trip unit.
The known configurations of the setting knob by way of a pin which engages in an engagement region of a tripping shaft and in particular the thermal shaft, also have the problem of a nonlinear translation of the rotary movement of the setting knob into a tangential or axial movement of the tripping shaft. Known adjustment mechanisms in this case have scaling of a rotary angle of at most 180°, wherein linear scaling along the rotation axis of the setting knob cannot be made possible, in particular since the axial movement of the tripping shafts is very low in a region of 0° or 180° of the rotary movement of the setting knob, in contrast to the axial movement of the tripping shaft in a region of 90° of the setting knob. Accordingly, linear scaling of the adjustment range of the setting knob would also not result in a linear axial movement or displacement of the tripping shaft.